Pollination of Nypa Fruticans (Wurmb.) in a South Florida Botanic Garden
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Journal of Pollination Ecology, 27(5), 2021, pp 57-64 POLLINATION OF NYPA FRUTICANS (WURMB.) IN A SOUTH FLORIDA BOTANIC GARDEN Imeña R. Valdes1-4, Joanna M. Tucker Lima1, Larry R. Noblick1 1Montgomery Botanical Center, 11901 Old Cutler Road, Coral Gables, FL 33156 USA 2Department of Biological Sciences, Florida International University, Miami, FL 33199 USA 3Program in Plant Biology and Conservation, Northwestern University, 633 Clark Street, Evanston, IL 60208 4Negaunee Institute for Plant Conservation Science and Action, Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, IL 60022 USA Abstract—When plants are removed from their native habitat, reproduction can be compromised if pollinators are absent, especially when plant-pollinator interactions are species-specific and the plant is self-incompatible. To avoid these pitfalls, botanic gardens often use hand pollination to ensure reproductive success of their living collections, an important aspect of ex-situ conservation. The nipa palm, Nypa fruticans, presents an interesting case study of pollination in a botanic garden and a plant’s ability to successfully reproduce outside its native range without assisted pollination. Nypa fruticans has been growing at Montgomery Botanical Center (MBC) in South Florida since 1984, but for years required hand pollination to produce viable fruit. A recent shift from hand pollination to unassisted pollination suggests that this palm has found an alternative to fertilize its flowers. We investigate possible pollinators and new opportunities for pollination outside the palm’s native range. Rather than the insects typically associated with N. fruticans pollination in its native range in Southeast Asia (i.e., flies and beetles), ants, specifically Paratrechina longicornis, were overwhelmingly the most abundant visitors to nipa palm inflorescences at MBC and likely represent an important pollinator or facilitator of pollination at the garden. Pollination research at botanic gardens complements in-situ field studies and provides important insights into the flexibility of pollination systems to achieve reproductive success outside a plant’s native range. Keywords: Nypa fruticans, plant-animal interactions, nipa palm, ant pollination, mangrove, phenology INTRODUCTION circumstances, exotic plants can successfully establish within natural plant communities, although sometimes to the Introduced exotic plants are not always able to reproduce detriment of local plant species (Sunderland & Morakinyo outside their native range unless they are self-compatible or 2002). Although the current literature on reproductive act as generalist species able to attract new pollinators from biology of exotic plant populations provides insights into the local area (Thompson & Knight 2018). Plants that rely on pollinator limitation and facilitation of exotic and naturalized specialized pollinators from their native habitat may be less plant populations, information regarding pollination of exotic integrated into exotic plant-pollinator networks, limiting non-naturalized plants, such as those found at botanic gardens successful reproduction outside their native range (Memmot and arboreta, is scarce (Thompson & Knight 2018). & Waser 2002; Thompson & Knight 2018); however, if a plant is served well by generalist pollinators, then it will likely Successful fruit production by plants grown in botanic overcome these obstacles (Memmot & Waser 2002). The gardens and arboreta is never guaranteed, but oftentimes the more generalized the pollinator, the more exotic plants it mission of such gardens involves advancing ex-situ includes in its diet (Memmot & Waser 2002). Razanajatovo conservation through seed production. To overcome the et al. (2015) suggest that plant species unable to maintain self- absence of native pollinators, gardens sometimes rely on hand sustaining populations may be pollinator limited. Across pollination to ensure successful reproduction, thus Europe, invasive plants living among natives were frequently maintaining seed production for distribution and storage to found to be visited by local native pollinators, and these conserve genetic resources for future generations. At pollinators often came to rely more on the invasive plants than Montgomery Botanical Center (MBC) in South Florida, the natives (Vilà et al. 2009). Sargent and Ackerly (2008) garden staff hand pollinate multiple rare and endangered claim that plants in small, isolated populations have the most species, including several cycad species (i.e., Cycas to gain from living among other plants that attract similar micronesica, Microcycas calocoma, Zamia lucayana) and tree pollinators, dubbed pollinator facilitation. Under these species, like Brownea capitella (Fabaceae). Nypa fruticans Wurmb. (Arecaceae), the mangrove palm commonly known as the nipa palm, is no exception. This species is native to Southeast Asia and grows mainly in brackish coastal areas. Received 04 July 2020, accepted 21 March 2021 First planted at MBC in 1984, the garden’s nipa palms *Corresponding author: [email protected] represent the only known healthy collection of this species growing in North America. For years, successful fruit set 57 58 VALDES ET AL. J Poll Ecol 27(5) required careful hand pollination, but in 2008 MBC scientists Nypa fruticans grows at four locations on MBC property, observed the first open-pollinated nipa fruits (Noblick et al. but thus far, successful fruit set has only been reported at two 2018). Shortly thereafter, a major freeze in 2010 destroyed all sites (Fig. 1). The garden palms were grown from seed developing nipa inflorescences, but with time N. fruticans collected in Malaysia and Indonesia in 1984 and 1998, recovered. Hand pollinations resumed for a number of years, respectively. The nipa palm has large pinnate leaves and a but the practice was discontinued in 2016. From 2017 subterranean stem with dichotomous branching and is onward, open-pollinated, viable nipa fruits have again been monoecious, displaying distinct male and female structures observed (Noblick et al. 2018). Has a mystery pollinator from within the same inflorescence (Fig. 1B; Uhl 1972). South Florida assumed the role of pollinator in N. fruticans? Nipa flowering is protogynous with the first male rachillae Have the nipa palms at MBC resorted to self-pollination to beginning to open a day after the onset of female anthesis successfully reproduce? In this study, we investigate the (Mantiquilla et al. 2013). Multiple male spikes on each reproductive biology of N. fruticans grown in a botanic inflorescence open in succession over the next several days and garden setting in South Florida, in order to identify the produce large amounts of pollen. Nipa palms rely on insects mysterious pollinator/s and discover how this palm species for pollination (Essig 1973; Mantiquilla et al. 2016), as the has been able to produce viable fruits without human spikey pollen grains are both sticky and heavy, making wind intervention after several years of dependence on hand transport highly unlikely (Fig. 2). During receptivity, pollination. stigmatic fluid is present on the three separate carpels that make up each female flower and are arranged in a tight, single MATERIALS AND METHODS head (Fig. 1B). Fruits mature over several months into a large, Study Site & Species Description heavy globular head (Fig. 1C), which may become so heavy in the wild that it topples into the water, where it breaks apart Montgomery Botanical Center (MBC; Coral Gables, into individual floating fruits that disperse and establish Florida, USA) is a research garden in South Florida that themselves at new locations. focuses on palms, cycads, and tropical conifers. The climate is humid and subtropical, and over the past 20 years the area Nypa fruitcans phenology experienced an average annual temperature of 25.3⁰C and Montgomery Botanical Center monthly phenology average annual rainfall of 1698 mm (NOAA 2020), having records from 1994–1997 were consulted to assess time of wet summers and dry winters. flowering. In addition, five inflorescences on two different Nypa fruticans is one of only two palms known to live plants were observed daily in 2018 for the duration of male and grow with their trunk submerged underwater; the other and female anthesis, and photographic images were taken to being Ravenea musicalis from Madagascar. The nipa palm is characterize the flowering cycle from pre-anthesis through native to estuarine mangrove vegetation and can be found in senescence. Each inflorescence was assigned a designated ID India and Sri Lanka, throughout Southeast Asia, and as far as (i.e., A, B, C, D, E). Both the male and female parts are bright Northern Australia. In the early 1900s, N. fruticans was yellow orange when they emerge, and fade to a white or tan introduced to Nigeria and has since spread and become color, respectively, over time. To characterize the invasive along the western coast of Africa (Numbere 2019; developmental stages of the inflorescence, we used color and Moudingo et al. 2020). Additional reports of established woodiness for the female phase, and we visually accessed the populations in areas of the Caribbean, including Trinidad, amount of pollen for the male phase based on color and Panama and Guyana, further attest to nipa’s ability to thrive coverage of the anthers. outside its native range (Noblick et al. 2018). FIGURE 1. Nypa fruticans at Montgomery Botanical Center (MBC) in Coral Gables, Florida: (A) healthy stand of N.